It was a powerful symbol of US friendship and support for the French, made from the tallest building in the US, which was built on the site of the 9/11 attacks on New York.

Its 124-metre spire is so large it can be seen across much of America's largest city and across the Hudson River in New Jersey.

"Today, and in the days ahead, New York will light One World Trade Centre in blue, white and red as we stand in solemn solidarity with the people of France," Governor Andrew Cuomo said.

"We join them in mourning those who were killed and in praying for those who were injured or lost loved ones. And we continue to stand side by side with them in our commitment to a free and peaceful world."

The French attacks are among the deadliest in the West since the September 11, 2001 terrorist attacks on New York, Washington and Pennsylvania.

Other US buildings also lit themselves in the colors of the French flag, including city hall in San Francisco and the Omni Hotel in Dallas, Texas.

Elsewhere in the city, French expats gathered in Union Square to express their solidarity with their compatriots. Some of the 50 or so demonstrators carried handmade signs reading 'Don't be afraid', and 'Pray for Paris', as they stood together in silence.